In recent years, in the manufacturing process of semiconductor device having a logic circuit or a non-volatile memory, a heating system using a laser has been used frequently instead of a heating system such as a lamp system used so far when heating the semiconductor device during a manufacturing process. Since laser annealing can apply a heat treatment at a high temperature in a short time and can prevent exposure of regions other than the target region for heating to a high temperature for a long time, it has advantages capable of decreasing damages to the semiconductor device due to heat and capable of improving the reliability of the device.
Laser annealing is used, for example, in a step of crystallizing an amorphous silicon film in an amorphous state by a heat treatment and forming a polysilicon film comprised of the amorphous silicon film in the manufacturing process of a phase-change random access memory (PRAM) by using a phase-change material such as a chalcogenide. Further, laser annealing is used also in a step of activating impurity in an impurity diffusion layer. Laser annealing is used instead of the lamp type heat treatment for preventing regions other than the region requiring a heat treatment in a PRAM from undergoing thermal loads.
The phase-change random access memory (hereinafter referred to as a phase-change memory) is a memory device of performing rewriting electrically by flowing a current to a phase-change material layer put between metal electrodes while utilizing the property of the phase-change material that an electric resistance is different by the order of several digits between an amorphous state and a crystalline state. A basic memory cell structure of the phase-change memory is a structure of combining a storage device (phase-change material layer) and a selection device.
Further, it is expected that the phase-change memory can perform write and read operations at a high speed substantially identical with that of dynamic random access memory (DRAM) although this memory is non-volatile, and since the cell area can be decreased to a level substantially identical with a flash memory, this is considered prospective as a next generation non-volatile memory.
Japanese Unexamined Patent Application Publication No. 2003-100085 disclosed a phase-change memory having a diode as a selection device.
Further, as a method of highly integrating a non-volatile memory that utilizes a resistance-change type device, Japanese Unexamined Patent Application Publication No. 2004-272975 discloses a memory array in which multiple memory cells having a transistor as a selection device for selecting a predetermined memory cell and a resistance-change type device connected in parallel are connected in series. Further, the capacity of the resistance-change type memory cell can be increased by stacking memory cells in multilayer as disclosed in Japanese Unexamined Patent Application Publication No. 2005-260014.
Further, Japanese Unexamined Patent Application Publication No. 2005-136213 describes a technique capable of suppressing abnormal operation of a thin film transistor (TFT) device formed by laser annealing and capable of separating a substrate and a device in a short time. In this technique, a heat insulating film comprised of a porous silicon oxide film having multiple gaps is disposed between a glass substrate and a TFT device on a glass substrate and the amorphous semiconductor layer forming a TFT device is crystallized by annealing at a high temperature for a long time by an excimer laser thereby forming a device of large carrier mobility. Japanese Unexamined Patent Application Publication No. 2005-136213 describes that a TFT device can be prevented from causing abnormal operation due to heat during operation by removing the heat insulating film after the annealing step for crystallization described above. However, the heat insulating film described therein is a silicon oxide film which is disposed with an aim of keeping a high temperature and this is not for preventing the layer below the heat insulating film from being heated by the laser. Further, the technique disclosed in Japanese Unexamined Patent Application Publication No. 2005-136213 is applied, for example, to a thin film transistor over a glass substrate and it contains no description of applying the same to a non-volatile memory or a logic circuit, etc.